Process for extruding filaments having asymmetric cross-section

ABSTRACT

A PROCESS TO REDUCE KNEEING DURING THE MELT SPINNING OF CONTINUOUS FILAMENTS THROUGH A T-SHAPED ORIFICE BY SELECTING DIMENSIONS OF THE ORIFICE SO THAT ITS EXTRUSION FACTOR IS WITHIN A DEFINED RANGE.

" Man-ch28,- 1972 B. H. SHEAMDIN 5 x PROCESS FOR EXTRUDING FILAMENTS HAVING ASYMMETRIC CROSS-SECTION Filed Feb. 26, 1970 3 Sheets-Sheet 1 F/GURE MOLTEN MATERIAL UNDER %EAT AND PRESSURE F/GURE 2 i "3 5 T HGURE 3 4W 1 i\ j l INVENTOR BEJAR HAZIM SHEMDIN March 28, 1972 B. H. SHEMDIN 3,652,753

PROCESS FOR EXTRUDING FILAMENTS HAVING ASYMMETRIC CROSS-SECTION s Sheets-Sheet 2 Filed Feb. 26, 1970 MOLTEN MATERIAL UNDER HEAT AND PRESSURE M hll F/GURE 4 INVENTOR BEJAR HAZIM SHEMDIN BY f' 'U..,.

B. H. SHEMDIN PROCESS FOR EXTRUDING FILAMEN'IS HAVING ASYMMETRIC CROSS-SECTION Filed Feb. 26, 1970 March 28, 1972 3 Sheets-Sheet 5 EXTRUSION PEREoRMANcEoE T-HOLED SPINNERETS 6 23m MT; 2 E5 8. m mmmomu mxhz soil 5258 o muzfimfimm maoumi N6 9.2m w b 0 LE AT SPIN'NERET FACE x=7o/|7 KNEE ANGLES (DEGREES) KNEE"ANG INVENTOR 0":70/13 KNEE ANGLES m w W 0 Bi m United States Patent O US. Cl. 264-177 F 4 Claims ABSTRACT OF THE DISCLOSURE A process to reduce kneeing during the melt spinning of continuous filaments through a T-shaped orifice by selecting dimensions of the orifice so that its extrusion factor is within a defined range.

BACKGROUND OF THE INVENTION This invention relates to a process of and apparatus for extruding filaments having asymmetrical cross-sections. It particularly relates to a process of and apparatus for extruding nylon 66 filaments having a generally T-shaped cross-section.

The formation of filaments from fiber-forming materials by extrusion of the material through an orifice is a generally accepted and well known practice in textile manufacture. Such practice in the past has been to a large degree concerned with the production of filaments which possess a round or nearly round transverse cross-section. It has been discovered, however, that desirable and advantageous physical and aesthetic properties can be obtained by producing filaments having modified transverse cross-sections, i.e., other than circular. By altering the filament cross-section it is possible to produce yarns with a mixture of properties normally associated with two distinct fibers. One example of this is a nylon yarn with filaments of triangular cross-section which has high abrasion resistance and tensile strength normally associated with nylon, combined with appearance and hand similar to natural silk. Textile filaments having a wide variety of cross-sectional configurations have been prepared. These cross-sections include ribbons, dumbbell or dogbone shapes, cruciform, crenulated, multilobal, e.g., trilobal, and the like shapes which exhibit various desirable properties when incorporated in textile goods. The following United States patents are deemed exemplary of patents showing various cross-sectional configurations: United States Patents 2,939,201; 2,939,202; 2,945,739; 3,038,237; 3,097,414; 3,097,416; 3,109,195; 3,121,040; 3,135,646 and 3,156,607. As disclosed in these patents, and in others not mentioned above, it has been discovered that such physical properties, for example, such as resiliency and stiffness, bulk and cover, hand and the like, and such optical properties, as dullness, sparkle, brightness and the like, as well as yarn frictional properties, are related to, and at least to some extent are controlled by the particular transverse cross-section of the filament.

While the spinning of noncircular filaments, as is readily seen from examining the above-mentioned patents, has for the'most part been concerned with the extrusion of symmetrically shaped filaments, it has also been suggested in the prior art to extrude noncircular asymmetrical filaments. Although the simplest way of producing noncircular filaments is to use noncircular holes for extrusion, another method'of obtaining filaments of noncircular cross-section is to fuse together a number of circular or ribbon shaped filaments to give composite filaments of various shapes. The spinning of filaments having an asymmetric T, pear or bell-shaped cross-section is disclosed, for example, in United States Patents 2,945,739; 3,038,237;"3,097,414; 3,121,040; and 3,135,646, all of ice which are abovementioned. While the T-shaped filament as described in United States Patents 3,038,237 and 3,097,414 is the result of a conjugate extrusion process through a single circular hole, the T-shaped filament formed in the remaining patents results from the extrusion of a single polymeric material through a T-shaped orifice.

Filaments having asymmetrical cross-sections also have desirable and advantageous physical and aesthetic properties as above-mentioned with respect to symmetrically shaped filaments. Further, asymmetrical cross-sections are desired at times to accentuate and/or minimize certain yarn properties as above-mentioned and to alter available yarn surface area so as to have a greater or lesser surface area available across a specific longitudinal portion of yarn.

However, the manufacture of asymmetrically-shaped filaments has not met with great success. This has been particularly true because of the propensity of filaments extruded through complex-shaped orifices, particularly those having asymmetrical-shaped holes, to knee or form doglegs and drips or blobs as hereinafter more fully described.

A filament is said to knee as the term is used herein, when the line of flow of the filament is bent out of the vertical back toward the spinnerette face at an angle with respect to the perpendicular to the spinnerette face. Such an angle formed between the normal to the spinnerette face and the plane of filament extrusion is called a knee angle. In some instances the filament is bent to such an extent that the filament-forming material, particularly on startup, bends back and touches the spinnerette face, leaving a drip or blob of filament-forming material on the spinnerette face in proximity to the orifice or orifices concerned. This blob can often partially block the spinning hole thereby interfering with filament formation. At other times, depending upon spinning hole spatial arrangement, two or more adjacent filaments can touch and coalesce as they are forced out of their normal flow path due to the kneeing effect. In greater detail, a partially blockedoff orifice can result in skinny filaments being produced, i.e. filaments of less than the desired denier thereby presenting the likelihood of a broken filament in subsequent drawing and/or other textile processing or may result in intermittent filament production, thereby resulting in yarn breakage during the spinning process. Additionally, severe kneeing distorts the cross-sectional shape of the extruded filaments.

While the actual occurrence of a blob or drip in some instances is normally forestalled by the routine procedure known as wiping in which the face of the spinnerette is cleaned, or reduced by such procedures as blanketing the face of the spinnerette with an inert gas to preclude oxidative degradation of the fiber-forming material such as dis closed in United States Patent 3,129,272, such procedures have not eliminated, or even reduced the problem of kneeing 'with which this invention is concerned.

One solution to the kneeing problem, at least with respect to T-shaped filaments, has been suggested by W. E. Beier and P. Paliyenko in their commonly assigned, c0- pending patent application Ser. No. 745,652, filed June 20, 1968. Although the unique arrangement of orifices therein described quite suitably solves the' problem, such spinnerettes are too costly to machine for most commercial applications. That is, the alternate solution disclosed therein, i.e. the provision of separate slots for the crossbar and stem of the split T orifices, While eliminating kneeing, results in a much more costly spinnerette because of the tolerances required between cross bar and stem sections. Other solutions to the kneeing problem have been less successful. The provision of smaller limb widths to increase jet velocity through the orifice still results in pronounced kneeing. Moreover, the enlarging of the stems in the T-shaped orifice, e.g. forming a fish-tail stem wherein the sides thereof diverge toward the end or forming a bobtail stem, i.e. providing an enlarged circle at the stem end, to counteract kneeing by increasing filament-forming material flow in the stem is a possible solution, but again it is difiicult to machine the holes to within the necessary tolerances.

Therefore, it is the primary object of this invention to avoid the disadvantages above-mentioned with respect to extruding filaments having a noncircular asymmetrical cross-section.

It is another object to eliminate kneeing and drips or blobs in extruding filaments through asymmetrically shaped spinnerette holes.

It is a further object to provide a process for extruding filamentary material for the formation of filaments having asymmetrically shaped cross-sections.

It is an additional object to extrude filaments having a T-shaped cross-section from orifices having a T-shaped crosssecion.

It is yet an additional object to provide a novel method for selecting a spinnerette plate having asymmetricallyshaped orifices through which filament kneeing is reduced.

It is still an additional object to provide novel spinnerettes for the production of asymmetrically-shaped filaments.

Other objects of the invention will be obvious to those skilled in the art from the detailed description hereinafter.

SUMMARY OF THE INVENTION In accordance with the invention, it has now been found that filament kneeing; and hence the deleterious effects thereof such as formation of polymer drips or blobs, change of filament shape and denier, and disruption of filament flow, occurring during extrusion of filamentforming materials through an asymmetrical cross-section spinnerette orifice; is markedly reduced and in many instances totally eliminated by extruding said material through a T cross-section orifice having only one plane of symmetry and wherein the stem extends normal from the centre of the cross bar, to produce non-kneeing filaments by selecting the peripheral dimension of said cross-section so that its extrusion factor, as defined more fully hereinafter, is about 0.65 to 0.90 and preferably about 0.75 to 0.80 and most preferably about 0.78. Even more particularly, both the stem and cross bar of the T-shaped orifice are substantially rectangular in shape.

DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a spinnerette plate showing a plurality of T-shaped orifices for spinning T-shaped filaments;

FIG. 2 is a partial cross-sectional view of a spinnerette head assembly including the spinnerette plate shown in FIG. 1 in across-section, the cross-section being taken on line 22, showing not only the filaments kneeing during their extrusion but formation of drips or blobs on the spinnerette face;

FIG. 3 is a greatly enlarged plan view of one of the T- shaped orifices in the spinnerette shown in FIG. 1;

FIG. 4 is a partial cross-sectional view of a spinnerette assembly and spinnerette plate containing T-shaped orifices according to the invention diagrammatically showing filaments being extruded without kneeing or the formation of drips or blobs; and

FIG. 5 is a graph showing the ratio of viscous resistances of the two limbs of various size T-shaped orifices plotted against the knee angle produced with such orifices.

DETAILED DESCRIPTION OF THE INVENTION Although certain features of the invention are described hereinafter in greater detail only with respect to a T- shaped orifice, it is not to be deemed so limited. Certain of the principles involved, particularly spinnerette selection, are applicable to the extrusion of filament-forming material through any asymmetrically shaped orifice. Illustrative of other asymmetrically shaped orifices with which certain embodiments of the invention may be practiced are K, Y, 71', and the like To be theoretically asymmetrical, an orifice must have no correspondence in size, shape, or relative position of parts thereof that are on opposite sides of an imaginary dividing line or median plane or that are distributed about a center or axis. With reference to the present invention and as the term asymmetrical is used in the spinnerette art, the orifices included in the invention must have at most one degree of planar symmetry, as hereinafter more fully explained. Contrary to the noncircular filaments described in the above-mentioned patents, particularly United States Patents 2,939,201 and 2,939,202, in which instances the filaments have a relatively high degree of planar symmetry, it is seen that the filament producing T-shaped orifice shown herein in FIG. 3 has a relatively low degree of planar symmetry. By degree of planar symmetry is meant the number of axes or straight lines that can be drawn in the plane of the filament crosssection and that will divide the filament cross-section into two equal parts, each being the mirror image of the other; or with reference to the filament, the number of planes which can be passed through the longitudinal axis of the filament to divide the filament into two equal parts, each part being the mirror image of the other. By this definition, a filament having an equilateral triangular cross-section has 3 degrees of planar symmetry. By this definition it is also seen that the orifice shown in FIG. 3 has one degree of planar symmetry as is shown by straight line xx. With respect, however, to straight line the T-shaped orifice is not symmetrical. It is this lack of planar symmetry (at most one degree of planar symmetry being present), in part, which leads to kneeing because of the unbalance in extrudate flow resulting thereform. During a conventional spinning process through a symmetrical spinnerette hole as defined, an extrudate velocity gradient occurs along the line of symmetry leading to kneeing as discussed more fully hereinafter.

Referring now more specifically to the drawing, there is shown in FIG. 1 a spinnerette plate 1 having a plurality of T-shaped orifices 2. The T-shaped orifices 2 have, as is more clearly shown in FIG. 3, a crossbar 3 and a stem or tail 4 which extends perpendicularly from the crossbar at its midpoint. The spinnerette plate 1 is attached to a conventional spinning head, designated generally by reference numeral 5, which is shown only in part in FIG. 2, for sake of clarity and because it forms no part of the present invention. T-shaped orifices 2 are arranged in a square-like pattern in the spinnerette plate, with an orifice 2 located at each corner of the square, as is shown in FIG. 1 of the drawing.

According to usual techniques, and as is diagrammatically shown in FIG. 2, molten material at a relatively high temperature and under pressure is caused to extrude from the orifice 2 to form filaments 6 having generally the shape of the T-shaped orifices 2 in the spinnerette plate 1.

Heretofore, in the extrusion of filaments 6 having a generally T-shaped asymmetrical cross-section, the filamentary material would knee, i.e. form an angle with respect to the perpendicular to the extrusion face 7 of the spinnerette plate 1 as is shown more clearly in FIG. 2. With some spinnerette plates the kneeing was discovered to be directed toward the crossbar 3 of the T- shaped orifice 2; however, with other spinnerette plates the kneeing was found to be directed away from the crossbar, that is toward the tail, of the T-shaped orifices. In some instances the angle of kneeing is so great that adjacent filaments touch one another and coalesce together to form a double filament. In many instances the filament-forming material, particularly upon startup of the extrusion, will bend back and touch the spinerette face 7 thereby forming a drip or blob of filament-forming material 8 thereon. With filament-forming material continually extruding from the orifices, the drip or mass or blob of filament-forming material 8 on the spinerette face 7 would grow and in some instances form double filaments 9 which eventually would, because of the weight thereof, cause the blob to detach itself and the filament to separate from the blob. In other instances the filamentforrning material became degraded due to heat and air oxidation and formed solid masses 10 of filament-forming material which blocked off the orifices, if not totally, at least in part. Spraying with silicone and other lubricants before and after extrusion and wiping the spinerettc face 7 during extrusion did not solve the kneeing problem or completely eliminate the formation of blobs.

It has been discovered, however, according to the invention, that with proper selection of orifice dimensions, particularly with respect with a T-shaped orifice so as to give an extrusion factor within the range of about 0.65 to 0.90 and preferably about 0.75 to 0.80 and most preferably about 0.78, kneeing of filaments 6 can be substantially eliminated as shown in FIG. 4.

It has been determined that kneeing can be controlled and virtually eliminated by constructing the T-shaped orifice so that the extrusion factor thereof as determined by the viscous resistance ratio of stem to crossbar is within the defined numerical range. Viscous resistance,

as used herein, is defined as the ratio of pressure drop across the particular section of the orifice to the volume rate of flow through the orifice and may be expressed as a function of the side wall dimensions of each rectangular segment of the'T-shaped orifice. Referring to FIG. 3 of the drawing, the viscous resistance of the crossbar section of the orifice can be expressed as a function of 1112 while the viscous resistance of the stem or tail portion of the T-shaped orifice is expressed as a function of cd In the preferred embodiments of the invention, kneeing through a T -shaped orifice wherein the crossbar and stem segments are essentially rectangular and wherein the stern segment is normal to the midpoint of the crossbar is markedly reduced by constructing said orifice so that its ration of ab /cd is about 0.65 to 0.90 or more preferably about 0.15 to 0.80 and most preferably about 0.78.

It isunderstood, of course, that similar mathematical formulae to express the viscous resistance as a function of orifice dimensions can be developed for different asymmetrical shapes which in turn are used to determine the extrusion factors thereof.

While as shown in FIG. 1 of the drawing the T-shaped orifices are arranged in a conventional square pattern, it is understood, of course, that any arrangement thereof is possible. The orifices may, e.g. be arranged in a parallelogram patternpwith a T-shaped orifice at each corner of the parallelogram. They may also be arranged in triangular patterns or in concentric circles as long as each hole receives the same amount of polymer per unit time.

The particular size and number of orifices, of course, depends upon the filament denier and the number of filaments desired to be extruded, as Well as the size spinnerette plate. Merely by way of example, however, a 4.00 inch spinnerette plate may contain 34 T-shaped orifices arranged in a conventional square pattern. The T-shaped orifice may have a rectangular crossbar .024 inch x .0033 inch and an integral rectangular stem .016 inch x .004 inch extending perpendicularly from the mid-point of the crossbar.

The dimensions of sides (a, b, c, d) of the T-shaped orifices 2 shown in FIG. 3 may vary considerably as long as the extrusion factor remains within the calculated range. In certain preferred aspects of the invention sides (a, c) which are the lengthwise dimensions of crossbar 3' and stem 4, respectively, may vary from about .005 to .007 inch to about .060 inch. Quite preferably side a varies from about .020 inch to about .036 inch. Sides (b, d) which represent the widthwise dimensions of the crossbar 3 and stem 4, respectively, may vary from as little as .0015 inch to as much as .007 inch. Desirably, however, sides b, d vary from about .0025 inch to about .004 inch, respectively.

The invention will be more fully described in the following examples which are deemed illustrative thereof. The T-shaped orifices are of the type in which the crossbar and stem portions are essentially rectangular in shape and in which the stem is normal to the crossbar at its mid point, as illustrated by FIG. 3 of the drawing.

Examples A and B illustrate conventional prior art spinning orifice dimensions.

Example A Polyhexamethylene adipamide (nylon 66) containing 30% by weight TiO delustrant and having a relative viscosity of about 40 was extruded according to usual techniques through a spinnerette plate having 34 T-shaped orifices.

The filaments extruded through the orifice were air quenched, collected in conventional fashion and then drawn at a draw ratio of about 4 to 1. A magnified crosssection of the drawn yarn shows the filaments to have substantially the appearance of a distorted T or pear shape, as is more clearly shown in the above-mentioned Paliyenko et al. copending application.

The dimensions in inches of the T-shaped orifices in the spinnerette plate used were: crossbar .036 x .004; stem .016 x .004.

The calculated extrusion fatcor is 2.25. The extrusion was accompanied with excessive kneeing and rather large blob formations caused by filament-forming material licking-back onto the spinnerette face.

Example B The same procedure was followed as in Example A except that a spinnerette plate having T-shaped orifices with crossbar dimensions in inches of .024 x .004 and stem dimensions of .016 x .004 was used. The extrusion factor is 1.33.

There was less kneeing than in Example A but the kneeing was still excessive for stable extrusion operation. Moreover, excessive blob formation resulted in partially blocked-off orifices.

Examples 1-22 The same spinning procedure except for extrusion velocity is used in each of the below examples as is used above in Example A. Spinnerette plates were used having the size T-shaped orifices noted.

The extrusion velocity of the filament-forming material in spinning the 70/17 yarn is twice that in spinning the 70/ 34 yarn.

Calculated extrusion factor values and respective determined knee angles are tabulated in Table 1.

Using the data on Table I and by plotting the knee angle caused by any particular size T-shaped orifice against the ratio of viscous resistances or extrusion factor as calculated, (ab /cd a smooth curve is obtained as is shown in FIG. 5 of the drawing. The letters a, b, c, and d represent the length and with dimensions of the sides of the crossbar and stem, respectively.

As shown by the graph in FIG. 5, wherein the Xs plot the knee angles for 70/17 extrusion and the Os plot the knee angles for 70/ 34 extrusion, the criterion for zero knee angle when using the T-shaped orifice is a ratio of viscous resistances (ab /cd of about 0.75 to 0.80. Such ratio allows the selection of any three dimensions of a T-shaped orifice, e.g. a, b, and c and the determination by calculation of the fourth dimension d which will result in balanced flow.

The discovery of non-kneeing with an extrusion factor of below 1 is highly unexpected since one skilled in the art would expect that the extrusion factor of 1, where balanced flow would be expected to occur through the spinnerette, would be the condition under which most stable extrusion conditions would be present and that kneeing would be present with an extrusion factor within the range of about 0.65 to 0.90. The reasons for this dis covery are not entirely understood but it is believed that a number of factors, in addition to the flow file through the spinning orifice, are involved.

TABLE I.KNEE ANGLES OF FILAMENTS Hole dimensions (.001) 70/17 70/34 Knee Knee Extrusion Cross- Examangle, Examangle, factor bar Tail pie degrees ple degrees 4 x 36 4 x 16 1 +40 12 +37 4 x 30 4 x 16 2 +34 13 +34 2. X 24 2. 5 x 16 3 +29 14 +30 4 x 24 4 X 16 4 +32 15 +23 3 X 20 3 X 16 5 +28 16 +25 3 X 24 3 x 20 6 +22 17 3 6 x 24 4 x 16 7 18 +14 3 x 3 x 20 8 +19 19 +19 4 X 20 4 X 20 9 +20 20 +21 3 3 x 24 4x 16 10 +1 21 1 3 x 24 4 x 16 11 --13 22 21 N.B. (4-) indicates kneeing away from the bar, indicates kneeing towards the bar.

Further experimentation establishes that a knee angle of :10 is acceptable for a continuous spinning operation. Therefore, the T-shaped orifice should have an extrusion factor value in the range of about 0.65 to 0.90 and preferably about 0.75 to 0.80 and most preferably about 0.7 8.

Knee angles are determined using a shadow graph technique.

This information is deemed applicable broadly to all types of fiber-forming materials. Illustrative of melt-spinna'ble polymers which may be used in the practice of this invention are the polyamides, such as polyhexamethylene adipamide, and polyepsiloncaprolactarn, and blends thereof, polyesters such as polyethylene terephthalate and other polymethylene terephthalates wherein the alcohol contains up to 10 carbon atoms such as those derived from ethylene glycol, terephthalate acid and up to 15 mol percent of some other dibasic acid, etc. In addition, plasticized melt-spinnable fibers such as acrylonitrile or c0- polymers containing at least 85 percent acrylonitrile may be utilized.

In preparing the filaments of the present invention, various additives may be included in the polymeric compositions. Yarn comprising filaments with the cross-section configuration specified in this invention are useful for a wide variety of textile products. They may be used to advantage in all sorts of woven materials including hosiery, lingerie and other light weight knit structures. They are useful as feed yarns for bulking processes such as the well known stutter box crimp process, the jet bulking process and the various fiase twist crimping techniques. The crimped product prepared by any of these processes may be used in sweaters, upholstery, carpets, underwear, shirting materials and the like. The crimped product may also be cut up into staple and recombined in the form of a staple yarn. These yarns of course are useful for preparing suiting materials, sweaters and a Wide variety of bulky textile materials.

It will be apparent that modifications of this invention will occur to persons skilled in the art.

What is claimed is:

1. A process for the melt extrusion of polyester, polyamide and polyacrylonitrile filament-forming material through a T-shaped orifice consisting of a substantially rectangular crossbar and a substantially rectangular stem extending perpendicularly therefrom at the mid-point of the crossbar, the improvement to reduce filament kneeing which comprises selecting the peripheral dimensions of said T-shaped orifice so that the extrusion factor of said orifice is about 0.65 to 0.90, said extrusion factor being the ration ab /cd wherein a is the length dimen sion of the crossbar, b is the length dimension of the stern, c is the width dimension of the crossbar, and d is the width dimension of the stem.

2. The process of claim 1 wherein said filament-forming, material is a polyamide.

3. The process of claim 2 wherein said extrusion factor is about 0.75 to 0.80.

4. The process of claim 3 wherein said extrusion factor is about 0.78.

References Cited UNITED STATES PATENTS 2/1963 Shealy 214171 2/1964 Shaw et al. 264177 F 6/1964 Hayden 2'64l77 F 11/1964 Jamieson 2.64-177 F 11/1964 Strachan 264-177 F FOREIGN PATENTS 5/1967 Japan 264-171 8/1968 Japan 264-Bicomp. Fiber JAY H. WOO, 'Primary Examiner US. Cl. X.R.- 

